In the group 1, there were 6 cases of stroke or transient ischemic attack within 30 days, including 3 cases of CYP2C19 gene deletion, 3 cases of CYP2C19 gene carriers, 2 cases of vertebrobasilar artery extracranial stenosis, and 4 cases of vertebrobasilar artery intracranial stenosis. Here, CYP2C19 is linked to transient ischemic attack.